The present invention relates generally to an integrated circuit (IC) design, and more particularly to a method for reducing leakage current in an IC chip.
In semiconductor technology, it is important to protect devices from mechanical damage and environmental contamination which may affect the proper operation of the devices. A conventional method commonly used for providing such protection is to directly coat the devices with a thin film of silicon nitride. Silicon nitride is commonly used since it provides resistance against wear and serves as a good barrier to sodium ions, which can penetrate into oxide layers of an IC chip and destroy their insulating properties. This layer of passivation silicon nitride is usually deposited at relatively low temperatures using a technique known as plasma enhanced chemical vapor deposition (PECVD). Under certain circumstances, a nitride layer alone is not enough for protecting its underlying devices. For instance, in physiological saline solution, under an applied electric field created from active components on an IC chip, the property of silicon nitride rapidly degrades. For this reason, in conventional methods, laminated layers of silicon oxide and silicon nitride may be used, wherein the silicon oxide can provide insulation to keep the current flow from the silicon nitride, while allowing the silicon nitride to protect the silicon oxide from sodium ions.
After formation of the silicon nitride and silicon oxide, a hydrogen-forming gas-annealing process is performed for driving hydrogen atoms into inter-metal dielectric layers of the IC chip to fix dangling bonds therein, thereby reducing their leakage current. However, the layer of silicon nitride acts as a barrier against the hydrogen diffusion, thereby lessening the effectiveness of the hydrogen-forming gas annealing process. For this reason, multiple stages of hydrogen-forming gas annealing process are often required in order to reduce the leakage current to an acceptable level. The multiple-stage annealing process is time-consuming and costly.
Therefore, desirable in the art of semiconductor manufacturing are methods for effectively and efficiently fabricating a semiconductor device with reduced leakage current.